Dramatic progress in the field of developmental biology in recent years has resulted from the application of a number of new approaches to classical problems, and led to the need for advanced courses to train new investigators to study those animal models, such as Xenopus, that have been taught for three years as part of an integrated set of courses at Cold Sprint Harbor in a number of areas of modern biology. This course provides extensive laboratory exposure to the biology and manipulation of embryos from the frog Xenopus laevis. Xenopus is a vertebrate uniquely suited for studies of early development, since large numbers of embryos, from fertilization onward, can easily be obtained. Development is rapid and the large size of the embryos facilitates their micromanipulation to allow analysis of such important issues as embryonic induction that are not feasible in mammalian embryos. The course is suited both for those who have a knowledge of molecular biology and developmental biology, but have had no experience with Xenopus, as well as those with some Xenopus experience who wish to increase t heir repertoire of techniques. The specific areas that will be covered are listed below; 1. Care and handling of Xenopus adults. Induction of ovulation, egg collection, testis isolation, and fertilization. 2. Stages of embryonic development and anatomy. 3. Whole mount in situ hybridization and immunohistochemistry. 4. Microinjection of eggs and oocytes with mRNA and DNA constructs. 5. Micromanipulation of embryos, including induction and transplantation assays. 6. Preparation and use of cell cycle extracts. It is anticipated that the basic organization of the course and much of the course material will remain unchanged during the proposed period of support, though new issues will be discussed and integrated into the laboratory as the field progresses.